KR102684617B1 - Automotive MIMO Radar Sensor - Google Patents

Abstract

The present invention relates to an automotive MIMO radar sensor having an antenna array (10) on a rectangular circuit board (16) with edges defining y and z directions, wherein the antenna array comprises transmit antennas ( It includes two or more arrays (TA1, TA2) of receiving antennas (TX) and two or more arrays (RA1, RA2) of receiving antennas (RX), and the transmitting antennas (TX) in each array are connected to each other in the z direction. The two arrays of transmit antennas (TA1, TA2) are offset from each other in the y direction, while the receive antennas (RX) in each array are offset from each other in the y direction. (RA1, RA2) are offset from each other in the z direction, wherein the automotive MIMO radar sensor has two arrays of transmitting antennas (TA1, TA2) positioned at two opposite edges of the circuit board 16. Arranged adjacently, two arrays of receive antennas RA1, RA2 are arranged adjacent to the remaining two edges of the circuit board 16, and an array of transmit and receive antennas in the central region of the circuit board 16. Between them, one or more high-frequency modules 18 are arranged on a circuit board.

Description

Automotive MIMO Radar Sensor

The present invention relates to an automotive MIMO radar sensor having an antenna array on a rectangular circuit board with edges defining y and z directions, wherein the antenna array includes two or more arrays of transmit antennas and receive antennas. comprising two or more arrays of antennas, wherein the transmit antennas in each array are offset from each other in the z direction, while the two arrays of transmit antennas are offset from each other in the y direction, and the receive antennas in each array are offset from each other in the y direction. While offset, the two arrays of receive antennas are offset from each other in the z direction.

Radar sensors are used in automotive driver assistance systems or vehicle autonomous driving systems for surrounding monitoring, in particular to measure the distance, relative speed and heading angle of other vehicles and likewise of stationary objects. In addition to detecting the azimuth of the object, that is, the angle between the line of sight to the object in the horizontal plane and the front direction of the vehicle, it is usually also necessary to detect the elevation angle, that is, the angle between the line of sight to the object and the horizontal plane. For example, the elevation angle makes it possible to determine the suitability of the target, that is, whether the target can be driven upward or downward (e.g., a bridge pier), or whether the target is an actual obstacle.

The azimuth and elevation angles of the target may be calculated from the amplitude difference and/or phase difference between the plurality of transmitting and/or receiving antennas of the antenna array. When multiple transmit antennas and multiple receive antennas are used, this is called a “Multiple-Input-Multiple-Output (MIMO) system.” This enlarges the (virtual) antenna aperture and thus improves angular accuracy and angular resolution.

For azimuth estimation, signals received by individual receive antennas must be evaluated in separate evaluation channels. To improve azimuth angular accuracy and angular resolution for a given number of evaluation channels, a spacing between the individual antennas is typically chosen, which is greater than half the wavelength of the radar propagation (λ/2). However, this may lead to ambiguities, which must be resolved by separate antenna arrays or by other methods, for example through longer-term tracking of located targets.

In typical FMCW radar sensors, the frequency of the transmitted radar signal is modulated in the form of a ramp. The received signal is mixed with components of the transmitted signal at the time of reception, so that an intermediate frequency signal is obtained with a frequency corresponding to the frequency difference between the transmitted signal and the received signal. Since this frequency difference depends on the signal propagation time due to frequency modulation and the relative speed of the object due to the Doppler effect, information on the spacing and relative speed of the object is obtained through multiple measurement cycles in which ramps with different slopes progress. Lose. The intermediate frequency signals recorded during one measurement cycle are converted via fast Fourier transform (FFT) into a spectrum in which each located object is characterized by peaks within specific frequency bins.

For angle estimation, the amplitude relationship and phase relationship of signals obtained from different receiving antennas, which depend on the angle of the object, are exploited in a characterized way. For example, the so-called DML function (Deterministic Maximum Likelihood Function) is calculated, which indicates how strongly the actually measured amplitude relationship and phase relationship for an object are correlated with the theoretical amplitude relationship and phase relationship for different angle hypotheses. . At this time, the angle hypothesis with the strongest correlation represents the best estimate of the object's angle.

In order to achieve as large an angular resolution as possible, the antenna array as a whole should have as large an aperture as possible, or at least as large a virtual aperture as possible, not only in the y direction but also in the z direction. Since the antenna array must therefore have relatively large dimensions, a circuit board of corresponding size is required. These circuit boards must be made of expensive materials suitable for high frequencies, resulting in increased costs.

The object of the present invention is to provide an antenna array that can be placed on a compact circuit board while enabling high angular resolution in azimuth and elevation.

According to the present invention, this task is accomplished by arranging two arrays of transmit antennas adjacent to two oppositely disposed edges of a circuit board and two arrays of receive antennas adjacent to the remaining two edges of a circuit board. This is achieved by arranging one or more high-frequency modules on the circuit board between the arrays of transmitting and receiving antennas in the central area of the circuit board.

In this arrangement, the outer borders of the antenna arrays form a rectangular frame that predefines the shape and dimensions of the rectangular circuit board, taking into account some minimum spacing between the circuit board border and the antenna patches. In this way, the space available on a rectangular circuit board can be optimally used for an antenna array with a large aperture in azimuth and elevation. In this case, there is a high degree of design freedom regarding the choice of precise spacings between the individual antennas, so that the antenna arrays can be configured according to the desired angular resolution and clarity of angle estimation.

There is space left in the central area of the circuit board that is not needed for antenna arrays. This available space is used for one or more high-frequency modules forming the transmitting and receiving circuits of the radar sensor. This further optimizes space utilization on the circuit board.

In one embodiment, the y direction is the azimuthal direction. In this case, for example, the receiving antennas may form two arrays extending along the upper and lower edges of the circuit board, while the transmitting antennas may form two arrays extending along the side edges of the circuit board. there is. In this case, in one embodiment, the transmit antennas may be located within an intermediate region between two arrays of receive antennas in the z direction. However, in another embodiment, the transmit antennas may be arranged side by side next to the arrays of receive antennas, so that the transmit antennas can utilize the entire space available on the circuit board in the z direction.

Below, embodiments are described in more detail with reference to the drawings.

1 is a schematic diagram of an antenna array of a radar sensor and an object to be located by this antenna array;
Figure 2 is a diagram similar to Figure 1 to illustrate different signal propagation paths;
Figure 3 is a front view of the antenna arrangement according to Figure 1, and
Figure 4 is a diagram of an antenna array according to a further embodiment.

Figure 1 shows an antenna array 10 and a control and evaluation device 12 of a radar sensor used to measure spacing, relative speed and direction angle of objects. By way of example, one individual object 14 is shown in this figure. For example, a radar sensor is installed in the front part of a car, not shown, and is used to specifically detect vehicles traveling ahead or other objects in the area in front of the car.

In particular, the radar sensor shown in this figure is formed for two-dimensional angle estimation in which not only the azimuth angle (θ) of the object 14 but also the elevation angle (ϕ) is estimated. In this case, the elevation angle (ϕ) is the line of sight (S) from the center of the radar sensor to the object 14; an azimuthal plane (horizontal plane) (P) spanning the vehicle forward (x) and lateral directions (y); It is defined as the angle between Azimuth (θ) is defined as the angle between the vertical projection of the line of sight (S) on the azimuth plane (P) and the forward direction (x). In this case, the radar sensor has angular resolution in the y direction (azimuth measurement) and in the z direction (elevation measurement).

In the example shown in this figure, the antenna array 10 includes two arrays “RA1”, “RA2” each having eight receive antennas (RX), formed on a rectangular circuit board 16; It includes two arrays “TA1” and “TA2” each having four transmit antennas (TX). The edges of the circuit board extend in the y and z directions.

The receiving antennas (RX) of each array are arranged at regular intervals on a straight line extending in the y direction. Accordingly, the receiving antennas form a so-called Uniform Linear Array (ULA). In this example, the transmit antennas TX are formed separately from the receive antennas (bistatic antenna concept) and are arranged offset with respect to the receive antennas not only in the y direction but also in the z direction.

In reality, the object 14, which is much further away from the antenna device 10 than in the schematic diagram of FIG. 1, is located within the transmit and receive lobes of all transmit and receive antennas, and therefore the transmit antennas TX A radar signal emitted from any one of the transmitting antennas and reflected by the object 14 may be received by each of the receiving antennas (RX).

By way of example, in FIG. 2 , one signal propagation path guided from the transmitting antenna of one of the transmitting antennas (TX) to the object 14 and from there back to the receiving antenna of one of the receiving antennas (RX) is shown as a solid line. One signal propagation path for another pair of transmitting and receiving antennas is shown as a broken line. In this case, it can be simply assumed that the radar signal starts from the phase center of the transmitting antenna (the center point of the corresponding antenna group) and proceeds toward the corresponding phase center of the receiving antenna.

At the center of the circuit board 16, a transmission unit 20 that generates transmission signals for transmission antennas; A receiving unit 22 that receives signals from receiving antennas (RX) in separated receiving channels, down mixes them into an intermediate frequency band, and transmits the intermediate frequency signals thus obtained to the control and evaluation device 12. ); A high-frequency module 18, for example, a Monolithic Microwave Integrated Circuit (MMIC), is arranged. Here, signals are recorded and digitized at a specific sampling rate over one measurement cycle. In this way, the digitized received signals are obtained and then further evaluated in the processor 24. The processor 24 also controls the radio frequency module 18 and, in particular, determines which of the transmit antennas TX to transmit and when.

Due to the offset of the transmit and receive antennas, the signal propagation paths, only two of which are shown by way of example in Figure 2, have different lengths for each pair of transmit and receive antennas. Due to the large gap between the antenna array 10 and the object 14, it can be generally assumed that the radar propagation is emitted as a plane wave and is also re-received as a plane wave, but the different lengths of the signal paths result in four reception This results in characteristic differences in the amplitude and phase of the signals received in the channels. These differences depend on the pair of transmit and receive antennas and the azimuth angle (θ) and elevation angle (phi) of the object 14. This effect is used when digitally evaluating data within the processor 24 to estimate the azimuth and elevation angles of an object.

In Figure 3 the antenna array 10 is shown in more detail. The transmit antennas (TX) as well as the receive antennas (RX) are each formed into an antenna group, extending vertically (in the z direction), in the example shown, each with eight antenna elements or patches 26. It consists of two columns. In-phase transmission signals provided from the transmitter 20 are supplied to the patches 26 from each of the transmit antennas TX. In this case, focusing of the emitted radar beam, in particular at the elevation angle, is achieved through the column-shaped arrangement of the patches 26 . The phase centers 28 of the antenna group are indicated by black squares in FIG. 3 .

In this example, the receiving antennas (RX) are likewise composed of patches 26 having the same arrangement as the patches in the transmitting antennas. For each individual receive antenna, the signals received by the individual patches 26 are integrated into a single signal via signal lines not shown, without changing the phase relationship between the signals of the different patches. Accordingly, in this example, the receiving lobes of the receiving antennas have the same shape as the transmitting lobes of the transmitting antennas.

The patches 26 of the transmitting and receiving antennas are square and have an edge length of λ/4, where “λ” is the (average) wavelength of the emitted radar waves. The spacing between patches within each antenna group is λ/2 not only horizontally but also vertically. The eight receiving antennas (RX) of each array “RA1”, “RA2” are arranged at intervals of 2λ, that is, the spacing in the y direction between the phase centers of two adjacent receiving antennas is 2λ. In the z direction, the antennas of each array are located at the same height. Accordingly, the upper edges of the antennas of the array "RA1" all have the same spacing "dz1" with respect to the upper edge of the circuit board 16, and correspondingly, the lower edges of the antennas of the array "RA2" all have the same distance "dz1" from the upper edge of the circuit board 16. It has the same spacing "dz2" for the border.

Arrays “TA1”, “TA2” of transmit antennas “TX” are located completely in the z-direction in the intermediate area between arrays “RA1”, “RA2” of receive antennas. Within each array, four transmit antennas are offset from each other in the z-direction, forming two pairs of antennas located at the same height in the y-direction. Accordingly, the left edges of the two outer antennas of the array "TA1" have the same spacing "dy1" with respect to the left edge of the circuit board 16. Likewise, the right edges of the two outer antennas of array “TA2” have the same spacing “dy2” with respect to the right edge of the circuit board. The offsets of the antennas relative to each other are different, but are integer multiples of λ/2 in the y-direction as well as the z-direction respectively. Additionally, the offsets in the two arrays “TA1” and “TA2” match, so array “TA2” is a shifted copy of array “TA1”.

In the first measurement cycle, transmission is performed only by one of the transmit antennas “TX” of one of the two arrays. Then, in the subsequent measurement cycle, if the transmission is carried out by the other antenna "TX2", what happens in this case with respect to wave propagation is that the transmission is carried out by the first antenna, but all reception by said two transmit antennas is carried out. This is equivalent to the case where antennas “RX” are offset by the same amount and in opposite directions. Now if all eight transmit antennas "TX" are activated in turn, a virtual receive array is obtained consisting of eight mutually offset copies of the two arrays "RA1" and "RA2". In this way, significant aperture enlargement is achieved not only in the y-direction but also in the z-direction, resulting in a clearer phase difference and thus clearer angular resolution.

Since the transmit antennas in arrays “TA1” and “TA2” are offset from each other in the y direction and by different widths in the z direction, the antenna spacings within the virtual array are not completely uniform. This gives design freedom to optimize the virtual array with respect to individual requirements. In general, an enlargement of the aperture is achieved as the gaps between the virtual antennas become larger, while the likelihood of ambiguity in angle measurement decreases as the gaps become increasingly filled.

In the antenna arrangement 10 shown in FIG. 3 , arrays of receive antennas RA1 and RA2 extend along the top and bottom edges of the circuit board 16, while arrays of transmit antennas TA1 and TA2 ) extends along the vertical edges of the circuit board. Therefore, the (real) arrays of receiving antennas RA1 and RA2 already have a large aperture in the y direction. Additionally, the arrays of transmit antennas TA1 and TA2 have the maximum spacing from each other that the width of the circuit board 16 allows in the y direction, so that the virtual aperture for angle measurements in azimuth is maximized. . The arrays of receiving antennas RA1 and RA2 have the maximum distance from each other that the height of the circuit board 16 allows in the z-direction, and the gaps between these two arrays are filled by the virtual arrays, so that For a given dimension of the circuit board 16, the opening area for angle measurement at the elevation angle is also maximized.

Since the remaining free space inside the circuit board 16 is used for the lines for the transmit and receive antennas and the high-frequency module 18, the space available on the circuit board 16 is optimally used, so that the circuit board ( 16), optimal performance is achieved for a given material cost.

4 , as a further example, arrays of transmit antennas TA1 and TA2 (outlined by dotted lines in the figure) extend across the entire available height of circuit board 16, and arrays of receive antennas RA1 A slightly modified antenna arrangement 10' is shown, arranged side by side next to the oppositely arranged ends of RA2). This allows further enlargement of the aperture surface in the z direction.

Claims (5)

A MIMO radar sensor for an automobile having an antenna array (10; 10') on a rectangular circuit board (16) with edges defining the y-direction and z-direction, wherein the antenna array is connected to one of the transmitting antennas (TX). It includes two or more arrays (TA1, TA2) and two or more arrays (RA1, RA2) of receiving antennas (RX), while the transmitting antennas (TX) in each array are offset from each other in the z direction. , the two arrays of transmit antennas (TA1, TA2) are offset from each other in the y direction, and the receive antennas (RX) in each array are offset from each other in the y direction, while the two arrays of receive antennas (RA1, RA2) is an automotive MIMO radar sensor that is offset from each other in the z direction,
Two arrays of transmit antennas (TA1, TA2) are arranged adjacent to two opposing edges of the circuit board 16, and two arrays of receive antennas (RA1, RA2) are arranged adjacent to two opposite edges of the circuit board 16. ), one or more high frequency modules 18 are arranged on the circuit board between the arrays of transmitting and receiving antennas in the central region of the circuit board 16,
Each of the two arrays of transmit antennas (TA1, TA2) includes two or more transmit antennas (TX) arranged with equal spacing (dz1, dz2) relative to the corresponding edge of the circuit board, and 2 of the receive antennas MIMO radar for automobiles, characterized in that each of the arrays (RA1, RA2) includes two or more receiving antennas (RX) arranged to have the same spacing (dy1, dy2) with respect to the corresponding edge of the circuit board. sensor. delete 2. An automotive MIMO radar sensor according to claim 1, wherein the arrays of transmit antennas (TA1, TA2) occupy only the space between two arrays of receive antennas (RA1, RA2) in the z direction. The method of claim 1, wherein the arrays of transmit antennas (TA1, TA2) are arranged outside the area of the arrays of receive antennas (RA1, RA2) in the y direction and the arrays of receive antennas (RA1, RA2) in the z direction. Overlapping with automotive MIMO radar sensors. 2. An automotive MIMO radar sensor according to claim 1, wherein the arrays of receive antennas (RA1, RA2) are ULA arrays.

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